One of the requirements of U.S. Federal Regulation FMVSS121 for highway tractor-trailer combinations (rigs) is that at least one trailer-mounted reservoir provides sufficient air entrapment for at least one parking brake release in order that the rig be movable from a parked position causing traffic difficulties. In principle, an air control system for brakes is needed that allows free flow of air to all air-operated devices under normal conditions but, in an emergency, seals off or isolates, e.g., the reservoirs and brake facilities associated with each axle of the trailer to prevent escape of air from that part of the system so that air is available for emergency movement of the rig from an undesired parking position to a position of safety. A system so arranged should store enough air to assure one or more emergency brake releases enabling a similar number of moves of the rig.
While there are various types of brake systems for operating the brakes of multiple-axle trailers, this invention is directed to that type which provides a service reservoir for each axle. In such a system, the facilities for assuring an emergency supply of air to the parking brake or spring chambers of the brake actuators involve, in the absence of the special fixture of the invention, a complication of line circuitry and many valves, especially check valves.
An object to this invention is to simplify and consolidate air-control and air-directing apparatus connecting a plurality of service reservoirs with emergency brake facilities into a multi-functional device or module capable of doing conventional functions as well as additional functions not presently realized in any system. Further objects are to make the brake system less expensive than the equipment it replaces, easier and less expensive to install, more readily accommodated within the trailer frame structure, and less prone to leakage through elimination of conduits and other elements of fluid circuitry. It is desired that the device comtemplated be capable of receiving air from the control or service line of the tractor as well as its supply line, and in case of its rupture of either line, be capable of distribution of air to spring chambers from any of the reservoirs carried on the trailer.